Cooling apparatus and electronic apparatus

ABSTRACT

A cooling apparatus includes: an evaporator, including a porous body, a vapor channel and a liquid channel separated by the porous body, to evaporate a working fluid in liquid phase; a condenser to condense the working fluid in vapor phase; a liquid reservoir tank to reserve the working fluid in the liquid phase; a vapor line connecting an outlet of the vapor channel in the evaporator and an inlet of the condenser; a liquid line connecting an outlet of the condenser and a first inlet of the liquid reservoir tank; a liquid supply line connecting an outlet of the liquid reservoir tank and an inlet of the liquid channel in the evaporator; a liquid return line connecting an outlet of the liquid channel in the evaporator and a second inlet of the liquid reservoir tank; and a liquid transport unit interposed in the liquid supply line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2010-268684, filed on Dec. 1, 2010, and Patent Application No. 2011-059735, filed on Mar. 17, 2011, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a cooling apparatus and an electronic apparatus.

BACKGROUND

One type of cooling apparatuses to cool heat-generating components, such as electronic components, provided in electronic apparatuses, e.g., computers, is cooling apparatuses based on gas-liquid two phase flow. Such cooling apparatuses achieve a higher cooling performance, by utilizing evaporative latent heat generated when working fluid in liquid phase (liquid-phase working fluid) evaporates into working fluid in vapor phase (vapor-phase working fluid).

An example includes a loop heat pipe (LHP) including an evaporator including a wick and a condenser, wherein the outlet of the evaporator and the inlet of the condenser are connected with a vapor line, while the outlet of the condenser and the inlet of the evaporator are connected with a liquid line, the loop heat pipe being filled with working fluid.

Such a loop heat pipe is capable of circulating the working fluid by means of the capillary force of the wick, thereby transporting the heat, without the need of a liquid transport pump, for example. Some cooling apparatuses are provided with liquid transport pumps on liquid lines, in order to ensure that the working fluid is circulated.

SUMMARY

A cooling apparatus of the present disclosure includes: an evaporator, including a porous body, a vapor channel and a liquid channel separated by the porous body, to evaporate a working fluid in liquid phase; a condenser to condense the working fluid in vapor phase; a liquid reservoir tank to reserve the working fluid in the liquid phase; a vapor line connecting an outlet of the vapor channel in the evaporator and an inlet of the condenser; a liquid line connecting an outlet of the condenser and a first inlet of the liquid reservoir tank; a liquid supply line connecting an outlet of the liquid reservoir tank and an inlet of the liquid channel in the evaporator; a liquid return line connecting an outlet of the liquid channel in the evaporator and a second inlet of the liquid reservoir tank; and a liquid transport unit interposed in the liquid supply line.

An electronic apparatus of the present disclosure includes: an electronic component provided over a circuit board; and a cooling apparatus to cool the electronic component, the cooling apparatus configured as described above, wherein the electronic component is thermally connected to the evaporator.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating the configuration of a cooling apparatus according to the present embodiment;

FIG. 2 is a schematic cross-sectional view illustrating the operation and effects of the cooling apparatus according to the present embodiment;

FIG. 3 is a schematic perspective view illustrating the configuration of a liquid reservoir tank and a liquid transport pump provided in the cooling apparatus according to the present embodiment;

FIG. 4 is a schematic perspective view illustrating a specific exemplary configuration of an evaporator provided in the cooling apparatus according to the present embodiment, and an exemplary configuration of an electronic apparatus including the same;

FIG. 5 is a schematic perspective view illustrating a specific exemplary configuration of the evaporator provided in the cooling apparatus according to the present embodiment;

FIG. 6 is a schematic view illustrating the configuration of a variant of a cooling apparatus according to the present embodiment;

FIG. 7 is a schematic perspective view illustrating a variant of the specific exemplary configuration of an evaporator provided in the cooling apparatus according to the present embodiment, and an exemplary configuration of an electronic apparatus including the same;

FIG. 8 is a schematic perspective view illustrating a variant of the specific exemplary configuration of the evaporator provided in the cooling apparatus according to the present embodiment;

FIG. 9 is a schematic perspective view illustrating a variant of a liquid transport pump provided in the cooling apparatus according to the present embodiment;

FIG. 10 is a schematic perspective view illustrating another variant of the specific exemplary configuration of an evaporator provided in the cooling apparatus according to the present embodiment, and an exemplary configuration of an electronic apparatus including the same;

FIG. 11 is a schematic view illustrating the configuration wherein an evaporator of another variant of a specific exemplary configuration is used in the cooling apparatus according to the present embodiment;

FIGS. 12A and 12B are schematic cross-sectional views illustrating the effects of an electronic apparatus including another variant of a specific exemplary configuration of the evaporator provided in the cooling apparatus according to the present embodiment;

FIG. 13 is a schematic perspective view illustrating a variant of the specific exemplary configuration of an evaporator provided in the cooling apparatus according to the present embodiment, and an exemplary configuration of an electronic apparatus including the same; and

FIG. 14 is a schematic cross-sectional view illustrating the issues of an evaporator provided in a conventional cooling apparatus.

DESCRIPTION OF EMBODIMENTS

An evaporator provided in a loop heat pipe as described above includes a casing 101 thermally connected to a heat-generating element 100, and a wick 102 in close contact with the inner wall of the casing 101, for example, as depicted in FIG. 14.

The wick 102 has a tubular shape, having a cavity 103 inside the wick 102. The wick 102 has an open end on the side (the right side in FIG. 14) of the inlet of the casing 101, while having a closed end on the side (the left side in FIG. 14) of the outlet of the casing 101. The cavity 103 inside the wick 102 communicates with a liquid line 104 connected to the inlet of the casing 101, defining a liquid channel through which liquid-phase working fluid flows. A groove 105 is defined between the inner wall of the casing 101 and the wick 102. This groove 105 communicates with a vapor line 106 connected to the outlet of the casing 101, defining a vapor channel through which vapor-phase working fluid flows. Particularly, the end of the wick 102, i.e., the wick 102 on the outlet side of the casing 101 is closed, defining a dead end of the cavity 103 inside the wick 102. In other words, the liquid channel in the evaporator is dead-ended.

In a loop heat pipe configured as described above, heat from the heat-generating element 100 is conveyed by the wick 102 to the liquid-phase working fluid, thereby heating the liquid-phase working fluid, which may result in vapor bubbles generated in the liquid-phase working fluid. This may cause dryout, making maintaining the cooling performance difficult.

Particularly, the end of the wick 102 contacts the vapor channel. Thus, liquid-phase working fluid within the liquid channel in the vicinity of the end of the wick 102 is heated to a temperature substantially similar to the temperature of the vapor-phase working fluid, which may accelerate formation of vapor bubbles. Furthermore, in thin-planer evaporators which are suited for efficiently cooling planer heat-generating elements generating considerable amount of heat, such as electronic components and a printed board, for example, heat from the heat-generating element 100 is more easily conveyed through the wick 102 to the liquid-phase working fluid. Thus, the temperature of the liquid-phase working fluid is increased, which accelerates generation of vapor bubbles in the liquid-phase working fluid. This tends to cause dryout, making maintaining the cooling performance difficult.

Furthermore, for an evaporator having a dead-ended liquid channel, even if a liquid transport pump is provided in a liquid line and liquid-phase working fluid is transported to the evaporator by the liquid transport pump, vapor bubbles generated in the liquid-phase working fluid cannot be removed.

Accordingly, it is desired that, even if vapor bubbles are generated in liquid-phase working fluid, these vapor bubbles are easily removed, thereby achieving a cooling apparatus providing a stable cooling performance.

Hereinafter, a cooling apparatus and an electronic apparatus according to embodiments will be described with reference to FIGS. 1-5.

The cooling apparatus according to the present embodiment is a cooling apparatus to cool a heat-generating element, such as electronic components included in an electronic apparatus, such as a computer (e.g., a server and personal computer), for example. Electronic apparatuses are sometimes referred to as electronic appliances. Examples of electronic components include a central processing unit (CPU) and an LSI chip, for example.

This cooling apparatus is a cooling apparatus based on gas-liquid two phase flow, which achieves a higher cooling performance, by utilizing evaporative latent heat generated when working fluid in liquid phase (liquid-phase working fluid) is evaporating into working fluid in vapor phase (vapor-phase working fluid).

Here, an embodiment will be described in the context of an exemplary cooling apparatus including a thin-planer evaporator suited for efficiently cooling a planer heat-generating element which generates considerable amount of heat, such as electronic components and a printed board (circuit board). Note that a thin-planer evaporator is sometimes referred to as a thin evaporator or a planer evaporator.

As depicted in FIG. 1, this cooling apparatus includes an evaporator 1 to evaporate liquid-phase working fluid, a condenser 2 to condense vapor-phase working fluid, a liquid reservoir tank 3 to reserve the liquid-phase working fluid, a vapor line 4 through which the vapor-phase working fluid flows, a liquid line 5 through which the liquid-phase working fluid flows, a liquid supply line 6, a liquid return line 7, and a liquid transport pump 8. Note that the liquid supply and liquid return lines 6 and 7 are simply referred to as “liquid lines” since they are liquid lines wherein the liquid-phase working fluid flows. While the liquid transport pump 8 is used in this embodiment, this is not limiting and any liquid transport units (liquid transport means) may be used which can transport the liquid-phase working fluid.

The outlet of vapor channel (vapor passage) 10 in the evaporator 1 is connected to the inlet of the condenser 2 with the vapor line 4. The outlet of the condenser 2 is connected to a first inlet 3A of the liquid reservoir tank 3 with a liquid line 5. An outlet 3C of the liquid reservoir tank 3 is connected to the inlet of a liquid channel (liquid passage) 11 in the evaporator 1 with the liquid supply line 6. The outlet of the liquid channel 11 in the evaporator 1 is connected to a second inlet 3B of the liquid reservoir tank 3 with the liquid return line 7. Additionally, the liquid transport pump 8 is interposed in the liquid supply line 6. More specifically, with the liquid supply line 6, the outlet 3C of the liquid reservoir tank 3 is connected to an intake opening 8A of the liquid transport pump 8, and a discharging opening 8B of the liquid transport pump 8 is connected to the inlet of the liquid channel 11 in the evaporator 1.

In this embodiment, the evaporator 1 includes a wick 12, and the vapor channel 10 and the liquid channel 11 separated by the wick 12, and a heat-generating element 9 (heat source) is thermally connected to the evaporator 1. In this embodiment, the vapor channel 10 is provided closer to the heat-generating element 9 in the evaporator 1, whereas the liquid channel 11 is provided farther to the heat-generating element 9 in the evaporator 1. Such a construction prevents heat from the heat-generating element 9 from being conveyed by the wick 12 to the liquid-phase working fluid, thereby reducing or eliminating generation of vapor bubbles in the liquid-phase working fluid. The wick 12 is a porous body. In this embodiment, the wick 12 is a porous body having a smaller heat conductivity. More specifically, the wick 12 is a porous body made from a resin. The porous body preferably has an average pore diameter of about 10 μm or less (preferably, about 6 μm or less). The average pore diameter may be determined using the mercury injection method.

In this embodiment, as depicted in FIG. 2, the evaporator 1 includes a casing 13 thermally connected to the heat-generating element 9, and a wick 12 in close contact with the inner wall of the casing 13, for example.

The wick 12 has a tubular shape, having a cavity 14 inside the wick 12. The wick 12 has open ends on the side (the right side in FIG. 2) of the inlet and on the side (the left side in FIG. 2) of the outlet of the casing 13. An inner cavity 14 of the wick 12 communicates with the liquid line 6 connected to the inlet of the casing 13 and the liquid line 7 connected to the outlet of the casing 13, defining the liquid channel 11 through which the liquid-phase working fluid flows.

In this manner, the end of the wick 12 on the outlet side of the wick 12, i.e., the inner cavity 14 of the wick 12, is not dead-ended and communicates with the liquid line 7 connected to the outlet of the casing 13. In other words, the liquid channel 11 in the evaporator 1 is not dead-ended, and communicates with the liquid lines 6 and 7 connected to the inlet and outlet sides of the evaporator 1.

A groove 15 is defined between the inner wall of the casing 13 and the wick 12. This groove 15 communicates with a vapor line 4 connected to the outlet of the evaporator 1, defining the vapor channel 10 through which vapor-phase working fluid flows.

In this manner, the liquid channel 11 in the evaporator 1 communicates with the liquid lines 6 and 7 connected to the inlet and outlet sides of the evaporator 1. In other words, the liquid channel 11 in the evaporator 1 includes an outlet, as well as an inlet, extending from the inlet to the outlet, and is connected to the liquid lines 6 and 7 on the inlet and outlet sides of the evaporator 1.

As depicted in FIG. 1, the liquid lines 6 and 7 connected to the inlet and outlet sides of the evaporator 1 are connected to the liquid reservoir tank 3, defining a circulation route (loop) for permitting circulation of the liquid-phase working fluid.

This facilitates the liquid-phase working fluid flowing through the liquid channel 11 in the evaporator 1 to circulate through the evaporator 1, rather than being retained in the evaporator 1.

As a result, as depicted in FIG. 2, even if vapor bubbles are generated in the liquid-phase working fluid in the liquid channel 11 inside the wick 12 due to the heat conveyed from the heat-generating element 9 through the wick 12 (i.e., heat leak), these vapor bubbles are easily removed from the liquid channel 11 inside the wick 12, by facilitating flow of the liquid-phase working fluid. This prevents dryout, thereby maintaining a cooling performance and achieving a stable cooling performance.

Particularly, the end of the wick 12 contacts the vapor channel 10. Thus, liquid-phase working fluid within the liquid channel 11 in the vicinity of the end of the wick 12 is heated to a temperature substantially similar to the temperature of the vapor-phase working fluid, which may accelerate formation of vapor bubbles. Furthermore, in thin-planer evaporators which are suited for efficiently cooling planer heat-generating elements generating considerable amount of heat, such as electronic components and a printed board, for example, heat from the heat-generating element 9 is more easily conveyed through the wick 12 to the liquid-phase working fluid. Thus, the temperature of the liquid-phase working fluid is increased, which accelerates generation of vapor bubbles. Particularly, in a thinner and wider (longer) evaporator 1, since a height of a liquid channel 11 inside the wick 12 is reduced, the liquid-phase working fluid is often prevented from entering below the vapor bubbles, which may result in dryout in the vicinity of the end of the wick 12, for example. In such a case, these vapor bubbles are easily removed from the liquid channel 11 inside the wick 12, thereby preventing dryout and achieving a stable cooling performance.

In the cooling apparatus as configured above, a portion of the liquid-phase working fluid supplied to the liquid channel 11 in the evaporator 1 leaks from the surface of the wick 12 facing the vapor channel 10 in the evaporator 1. In other words, the portion of the liquid-phase working fluid flowing through the inlet of the liquid channel 11 in the evaporator 1 leaks to the vapor channel 10 side in the evaporator 1 through the wick 12.

The liquid-phase working fluid leaking from the surface of the wick 12 is evaporated (vaporized) into vapor-phase working fluid by the heat conveyed from the heat-generating element 9 through the casing 13, since a portion of the wick 12 thermally contacts with a portion of the casing 13 of the evaporator 1.

As depicted in FIG. 1, the leaked and evaporated vapor-phase working fluid flows into the condenser 2 through the vapor channel 10 in the evaporator 1 and the vapor line 4. Thereafter, the heat of the vapor-phase working fluid is removed in the condenser 2 and the vapor-phase working fluid is cooled to condense (liquidity) into liquid-phase working fluid.

The condensed liquid-phase working fluid flows into the liquid reservoir tank 3 through the liquid line 5. In other words, the liquid-phase working fluid from the condenser 2 flows from the first inlet 3A of the liquid reservoir tank 3 into the liquid reservoir tank 3.

The liquid-phase working fluid reserved in the liquid reservoir tank 3 is supplied to the liquid channel 11 in the evaporator 1 through the liquid supply line 6 by the liquid transport pump 8.

Thus, the working fluid refluxes in a circulation route defined by the liquid reservoir tank 3, the liquid supply line 6, the evaporator 1, the vapor line 4, the condenser 2, and the liquid line 5.

On the other hand, the remaining portion of the liquid-phase working fluid supplied to the liquid channel 11 in the evaporator 1 flows through the outlet of the liquid channel 11 in the evaporator 1 and returns to the liquid reservoir tank 3 through the liquid return line 7. More specifically, the remaining portion of the liquid-phase working fluid flowing through the inlet of the liquid channel 11 in the evaporator 1 remains in liquid phase, or a portion of the liquid-phase working fluid is vaporized into vapor-phase working fluid by heat from the wick 12, thereby forming mixed-phase working fluid, which flows through the outlet of the liquid channel 11 in the evaporator 1, and returns to the liquid reservoir tank 3 through the liquid return line 7.

In this manner, the working fluid refluxes in a circulation route defined by the liquid reservoir tank 3, the liquid supply line 6, the evaporator 1, and the liquid return line 7.

This cooling apparatus achieves a significantly higher cooling performance (heat-radiation characteristic) since it can efficiently transport heat from the heat-generating element 9 by means of both evaporative latent heat and sensible heat.

More specifically, a portion of the heat conveyed from the heat-generating element 9 to the evaporator 1 is stored in vapor-phase working fluid as evaporative latent heat (vaporization heat), when the liquid-phase working fluid leaking to the vapor channel 10 outside the wick 12 vaporizes, and is then transported to the condenser 2 through the vapor line 4, undergoing heat-radiation.

Furthermore, a portion of the heat conveyed from the heat-generating element 9 to the evaporator 1 is transported to the liquid channel 11 through the wick 12, and is stored in the liquid-phase working fluid in the liquid channel 11 as sensible heat. If the temperature of the liquid-phase working fluid exceeds its saturation temperature, a portion of the liquid-phase working fluid phase-changes into vapor phase.

In this cooling apparatus, since working fluid flowing through the liquid channel 11 is circulated by the liquid transport pump 8, liquid-phase working fluid at an elevated temperature is transported to the liquid reservoir tank 3 through the liquid return line 7. Through the liquid return line 7, heat is radiated from the surface of the liquid return line 7, for example. In this manner, liquid-phase working fluid at an elevated temperature, in addition to vapor-phase working fluid, is discharged from the evaporator 1, rather than being retained in the evaporator 1. In other words, the entire heat conveyed from the heat-generating element 9 to the evaporator 1 is transported outside the evaporator 1, thereby radiating heat substantially completely. Thus, it is possible to maintain the evaporator 1 at a lower temperature, thereby achieving a significantly higher cooling performance.

As set forth previously, this cooling apparatus is a loop heat pipe (LHP) including an evaporator 1 including a wick 12 and a condenser 2, wherein the outlet of the evaporator 1 and the inlet of the condenser 2 are connected with the vapor line 4, while the outlet of the condenser 2 and the inlet of the evaporator 1 are connected with the liquid lines 5 and 6, the loop heat pipe being filled with working fluid.

Such a loop heat pipe is capable of transporting the heat by circulating working fluid by capillary force of the wick 12 provided in the evaporator 1, thereby transporting the heat. In other words, heat can be transported to the condenser 2 by means of the vapor pressure inside the evaporator 1.

In this embodiment, the loop heat pipe configured as described above is further provided with a liquid reservoir tank 3, a liquid return line 7, and a liquid transport pump 8.

In this embodiment, one end of the liquid return line 7 is connected to the outlet of the liquid channel 11 in the evaporator 1, while the other end of the liquid return line 7 is connected to the liquid reservoir tank 3. More specifically, the outlet of the liquid channel 11 in the evaporator 1 is connected to a second inlet 3B of the liquid reservoir tank 3 with the liquid return line 7. Furthermore, the liquid reservoir tank 3 and the liquid transport pump 8 are interposed in the liquid lines 5 and 6 connecting the outlet of the condenser 2 and the inlet of the evaporator 1. More specifically, the liquid line 5 and the liquid supply line 6 are provided as liquid lines connecting the outlet of the condenser 2 and the inlet of the evaporator 1, wherein the outlet of the condenser 2 and the first inlet 3A of the liquid reservoir tank 3 are connected with the liquid line 5, while the outlet 3C of the liquid reservoir tank 3 and the inlet of the liquid channel 11 in the evaporator 1 are connected with the liquid supply line 6. Additionally, the liquid transport pump 8 is interposed in the liquid supply line 6.

This loop heat pipe has routes for circulating working fluid: a first route (first loop) circulating through the liquid reservoir tank 3, the liquid supply line 6, the evaporator 1, the vapor line 4, the condenser 2, and the liquid line 5; and a second route (second loop) circulating through the liquid reservoir tank 3, the liquid supply line 6, the evaporator 1, and the liquid return line 7. In such a configuration, the working fluid flowing through the first route is circulated primarily by means of the capillary force of the wick 12, whereas the working fluid flowing through the second route is circulated primarily by the liquid transport pump 8.

When an evaporator as a heat-receiving unit and a condenser as a radiator unit were distant apart, defining a longer heat transportation distance, or when a liquid channel were narrow in a thin evaporator, such as in a micro channel, for example, pressure loss in the circulation routes would be increased. In such a configuration, a larger liquid transport pump would be required (or a plurality of liquid transport pumps are required).

In contrast, in this embodiment, the second route to circulate liquid-phase working fluid by means of the power of the liquid transport pump 8 is shorter. Furthermore, since this cooling apparatus utilizes evaporative latent heat, the amount of liquid-phase working fluid (smaller amount of fluid) supplied to the evaporator 1 by the liquid transport pump 8 is reduced, as compared to a cooling apparatus employing sensible heat in a single phase.

Thus, since only a smaller amount of working fluid is required to be circulated through a shorter circulation route, the pressure loss in the circulation route is reduced and accordingly a smaller liquid transport pump 8 (or a smaller number of liquid transport pumps 8) can be used. In other words, a sufficient amount of working fluid can be circulated even with a smaller liquid transport pump 8, without requiring a larger liquid transport pump (or without requiring an increasing number of liquid transport pumps).

In addition, for an evaporator 1 of a thinner and wider thin-planer evaporator, it is difficult to evaporate liquid-phase working fluid by evenly impregnating the liquid-phase working fluid across a larger-area wick 12. In such an evaporator, circulation of the working fluid is unstable since the wick 12 is partially dried out, for example. Provision of a liquid transport pump 8 can eliminate such an issue, thereby achieving a stable cooling performance. Consequently, with the assistance of a smaller liquid transport pump 8, it is possible to efficiently cool a planer heat-generating element that generates considerable amount of heat, such as electronic components and a printed board, using a thin-planer evaporator. This means that efficient cooling of a planer heat-generating element can be achieved, by reducing the thickness (height) of an evaporator 1 (reducing the height while increasing the area) and reducing the size of a liquid transport pump 8 (or using a smaller number of liquid transport pumps 8; size reduction and power conservation). Note that the reduction in the size and/or number of a liquid transport pump(s) 8 translates into reduction in the capacity of the liquid transport pump(s) 8.

Furthermore, even when an evaporator 1 as a heat-receiving unit and a condenser 2 as a radiator unit are distant apart and thus the heat transportation distance is increased, a smaller liquid transport pump 8 can be used. More specifically, even when the evaporator 1 and the condenser 2 are distant apart and thus the heat transportation distance is increased, heat can be transported to the condenser 2 that is distant apart with an assistance of the capillary force of the wick 12 provided in the evaporator 1 and the vapor pressure in the evaporator 1. Thereby, a cooling apparatus having an efficient and higher-performance thin-planer evaporator 1 can be achieved.

In this embodiment, the liquid reservoir tank 3 has a height sufficient to separate between liquid-phase working fluid and vapor-phase working fluid, as depicted in FIG. 3. In other words, the liquid reservoir tank 3 has a height sufficient to define a space above liquid-phase working fluid, while reserving the liquid-phase working fluid in the liquid reservoir tank 3.

Particularly, the second inlet 3B of the liquid reservoir tank 3 is preferably provided farther from the outlet 3C of the liquid reservoir tank 3 than the first inlet 3A. More specifically, the liquid reservoir tank 3 preferably includes an outlet 3C to which the liquid supply line 6 is connected, a first inlet 3A which is provided in the vicinity of the outlet 3C and to which the liquid line 5 is connected, and a second inlet 3B which is provided farther from the outlet 3C and to which the liquid return line 7 is connected.

In this embodiment, the outlet 3C of the liquid reservoir tank 3 is provided in a lower position on one wall 3X of the liquid reservoir tank 3, i.e., the wall in the downstream in the circulation direction of the working fluid. Furthermore, the second inlet 3B of the liquid reservoir tank 3 is provided on another wall 3Y opposite to the one wall 3X of the liquid reservoir tank 3, i.e., the wall in the upstream in the circulation direction of the working fluid. Furthermore, the first inlet 3A of the liquid reservoir tank 3 is provided on a wall 3Z perpendicular to the one and another walls 3X and 3Y of the liquid reservoir tank 3. In this embodiment, the liquid line 5 connected to the first inlet 3A of the liquid reservoir tank 3 extends inside the liquid reservoir tank 3 such that one end thereof is located in the vicinity of the outlet 3C of the liquid reservoir tank 3.

In this manner, liquid-phase working fluid not evaporated in the evaporator 1, flowing through the liquid channel 11 in the evaporator 1, and returned to the liquid reservoir tank 3 via the liquid return line 7 is introduced into the liquid reservoir tank 3 in a position as far from the outlet 3C of the liquid reservoir tank 3 as possible. Thereby, it is ensured that vapor bubbles, if present, are removed from liquid-phase working fluid.

On the other hand, liquid-phase working fluid condensed in the condenser 2 and returned to the liquid reservoir tank 3 through the liquid line 5 is introduced into the liquid reservoir tank 3 in a position that is as close to the outlet 3C of the liquid reservoir tank 3 as possible. Thereby, liquid-phase working fluid cooled in the condenser 2 without vapor bubbles is more quickly discharged from the outlet 3C of the liquid reservoir tank 3, and then is supplied to the evaporator 1, by the liquid transport pump 8.

Furthermore, even when liquid-phase working fluid containing vapor bubbles flows into the liquid reservoir tank 3, by disposing the outlet 3C of the liquid reservoir tank 3 in the lower position, vapor bubbles emerges to the upper position of the tank 3 and are prevented from being introduced into the working fluid flowing through the outlet of the liquid reservoir tank 3.

A cooling apparatus configured as described above is used to cool electronic components 21 included in an electronic apparatus 20, such as a computer, for example (see FIG. 4). In this case, the electronic apparatus 20 includes the electronic components 21 and a cooling apparatus 22 configured as described above (see FIG. 1) to cool these electronic components 21, wherein the electronic components 21 are thermally connected to the evaporator 1 included in the cooling apparatus 22.

In this case, the electronic components 21 may contact at least one of the front face (top side) and the back face (bottom side) of the evaporator 1 included in the cooling apparatus 22, via a circuit board 23, such as a printed board (see FIG. 4), or the electronic components 21 may directly contact at least one of the front and back faces of the evaporator 1 included in the cooling apparatus 22.

For example, a circuit board 23, such as a printed board, including the electronic components 21 mounted thereon, may be provided on at least one of the front and back faces of the evaporator 1 included in the cooling apparatus 22 (see FIG. 4). Alternatively, the evaporator 1 included in the cooling apparatus 22 may be disposed on the front faces of electronic components provided on a circuit board, such as a printed board. Alternatively, electronic components provided on a circuit board, such as a printed board, may be disposed such that the electronic components directly contact the front face of the evaporator 1 included in the cooling apparatus 22. An circuit board having electronic components mounted thereon receives heat from the electronic components as a heat-generating element. Such a circuit board is referred to as a plate heat-generating element or planer (flat plate) heat-generating element, since the entire circuit board is generating heat and it has a plate shape.

Hereinafter, a description will be made in the context of an exemplary the electronic apparatus 20, including a planer evaporator 1 to efficiently cool a planer heat-generating element 24, provided on both the front and back faces of the planer evaporator 1, with reference to FIGS. 4 and 5.

As depicted in FIG. 5, the evaporator 1 includes, a casing 13 (metal casing, in this embodiment) including a liquid inlet 13A, a liquid outlet 13B, and a vapor outlet 13C, a wick 12 being a porous body made from a resin, a liquid inlet-side manifold 25 made from a resin, and a liquid outlet-side manifold 26 made from a resin.

In this embodiment, the wick 12 includes a planer portion 12A, a plurality of projections 12B provided both on the front and back faces of the planer portion 12A, extending in a first direction, and arranged in parallel to each other, and a plurality of through holes 12C formed inside the planer portion 12A, extending in a second direction perpendicular to the first direction, and arranged in parallel to each other.

In this embodiment, as depicted in FIG. 4, the back faces of two resin porous plates 12AX that have a plurality of projections 12B each having a rectangular cross section on the front face side, and have a plurality of recesses 12CX each having a semicircular cross section on the back face side, are bonded together, to form the wick 12 including the planer portion 12A, the projections 12B, and the through holes 12C.

Thereby, once the wick 12 is enclosed in the casing 13, the front faces of the plurality of projections 12B provided on the front face come in contact with the top wall of the casing 13, while the front faces of the plurality of projections 12B provided on the back face come in contact with the bottom wall of the casing 13.

Thereby, a plurality of regions surrounded by the top wall of the casing 13, the planer portion 12A of the wick 12, and the projections 12B define a plurality of through holes which extend in the first direction and are arranged in parallel to each other, defining the vapor channels 10 through which vapor-phase working fluid flows. More specifically, the spaces between the plurality of projections 12B provided on the front face of the wick 12 define grooves 15, and the tops of the plurality of grooves 15 are closed with the top wall of the casing 13, defining the vapor channels 10.

Similarly, a plurality of regions surrounded by the bottom wall of the casing 13, the planer portion 12A of the wick 12, and the projections 12B define a plurality of through holes which extend in the first direction and are arranged in parallel to each other, defining the vapor channels 10 through which vapor-phase working fluid flows. More specifically, the spaces between the plurality of projections 12B provided on the back face of the wick 12 define grooves 15, and the tops of the plurality of grooves 15 are closed with the bottom wall of the casing 13, defining the vapor channels 10.

Thus, in this embodiment, the evaporator 1 includes a plurality of vapor channels 10 on opposite sides thereof, sandwiching the planer portion 12A of the wick 12.

Furthermore, the plurality of through holes 12C formed within the planer portion 12A of the wick 12 define the liquid channels 11 through which liquid-phase working fluid flows. In other words, the vapor channels 10 provided over the front and back face of the planer portion 12A of the wick 12, and the liquid channels 11 formed within the planer portion 12A of the wick 12, are separated by the planer portion 12A of the wick 12. The liquid-phase working fluid supplied to the liquid channels 11 by the capillary force of the wick 12 passes through the pores in the wick 12 to leak to the vapor channel 10 side.

Furthermore, in this embodiment, the plurality of liquid channels 11 extend in the second direction perpendicular to the first direction, and are arranged in parallel to each other. In other words, in this embodiment, the liquid channels 11 and the vapor channels 10 extend in the directions perpendicular to each other. Therefore, as will be described below, the liquid outlet 13B and the vapor outlet 13C can be provided in the walls of the evaporator 1 which are perpendicular to each other. In other words, the liquid return line 7 and the vapor line 4 can be connected to the walls of the evaporator 1 which are perpendicular to each other. Thereby, it is ensured that the liquid-phase working fluid flowing through the liquid channels 11 and the vapor-phase working fluid flowing through the vapor channels 10 are separated with a simpler configuration, thereby guiding the liquid-phase working fluid to the liquid return line 7, and the vapor-phase working fluid to the vapor line 4.

Thus, in this embodiment, the evaporator 1 has a three-layered structure wherein a vapor channel layer including the plurality of vapor channels 10, a liquid channel layer including the plurality of liquid channels 11, and a vapor channel layer including the plurality of vapor channels 10 are stacked. In other words, the two outer layers define vapor channel layers, and the one inner layer sandwiched between the two vapor channel layers defines a liquid channel layer. Thus, the evaporator 1 includes the vapor channels 10 (first vapor channels) provided at the top of the wick 12, the vapor channels 10 (second vapor channels) provided at the bottom of the wick 12, and the liquid channels 11 inside the wick 12. In this embodiment, for a planer evaporator 1, the outer vapor channel layer preferably has a height of about 1 mm or less, while the inner liquid channel layer preferably has a height of about 2 mm or less.

Specifically, in this embodiment, the wick 12 is a porous body made from polytetrafluoroethylene (PTFE) resin having a porosity of about 40% and an average pore diameter of about 5 μm. Furthermore, the wick 12 has a thickness of about 4 mm, which is a thickness from the ends of the projections 12B on the front face to the ends of the projections 12B on the back face, and a planer dimension of about 110 mm×about 110 mm. Furthermore, the vapor channels 10 have a cross section of about 1 mm×about 1 mm, and the plurality of vapor channels 10 are arranged in parallel to each other with a spacing (pitch) of about 2 mm. Furthermore, the liquid channels 11 have a cross-sectional diameter of about 1 mm, and the plurality of liquid channels 11 are arranged in parallel to each other with a spacing (pitch) of about 2 mm. Furthermore, the minimum thickness of the planer portion 12A of the wick 12 separating between the vapor channels 10 and the liquid channels 11 is about 0.5 mm.

Furthermore, the wick 12 configured as described above includes a liquid inlet-side manifold 25 attached to one side of the liquid channels 11, and a liquid outlet-side manifold 26 attached to the other side, and is enclosed in the casing 13, as depicted in FIG. 5. More specifically, the casing 13 includes a liquid inlet 13A on one wall, a liquid outlet 13B on the wall opposing to the one wall, and a vapor outlet 13C on the wall perpendicular to the one wall. The wick 12 having the liquid inlet-side manifold 25 and the liquid outlet-side manifold 26 attached thereto is enclosed in the casing 13 such that its liquid channels 11 extend from the one wall toward the wall opposing to the one wall of the casing 13. As a result, the vapor channels 10 of the wick 12 extend from the wall perpendicular to the one wall to the opposing wall. Furthermore, the opening of the liquid inlet-side manifold 25 and the liquid supply line 6 are connected to the liquid inlet 13A of the casing 13, while the opening of the liquid outlet-side manifold 26 and the liquid return line 7 are connected to the liquid outlet 13B, and the vapor line 4 is connected to the vapor outlet 13C. In this manner, the wick 12 and the like are enclosed in the casing 13, and the liquid supply line 6 and the like are attached to the casing 13 such that the liquid supply line 6, the liquid inlet-side manifold 25, the liquid channels 11 of the wick 12, the liquid outlet-side manifold 26, and the liquid return line 7 communicate with each other, while the vapor channels 10 of the wick 12 and the vapor line 4 communicate with each other.

Specifically, in this embodiment, the liquid inlet-side manifold 25 and the liquid outlet-side manifold 26 are resin manifolds made of MC nylon, for example. Furthermore, the casing 13 is a copper casing having a wall of a thickness of about 0.3 mm. Here, the casing 13 is manufacturing by fabricating a container, made of copper, having an opening at the top, and a lid, made of copper, to cover the top opening; enclosing the wick 12 and so forth in the container; and welding the container and the lid together to seal the casing 13.

Then, as depicted in FIG. 4, on the two faces, i.e., on the top and the bottom faces, of the planer casing 13 of the evaporator 1 configured as described above, a printed board 23 having a plurality of electronic components 21 (heat-generating components) mounted thereon, i.e., a planer heat-generating element 24, is disposed. In other words, on the two faces, i.e., on the top and the bottom faces, of the casing 13 of the planer evaporator 1, the planer heat-generating element 24 is thermally connected.

Specifically, the top face of the casing 13 of the planer evaporator 1 and the back face of the planer heat-generating element 24, i.e., the back face of the printed board 23 having the plurality of electronic components 21 mounted thereon, are in a close contact with a thermal grease, such that heat from the planer heat-generating element 24 is conducted to the planer evaporator 1. Similarly, the bottom face of the casing 13 of the planer evaporator 1 and the back face of the planer heat-generating element 24, i.e., the back face of the printed board 23 having the plurality of electronic components 21 mounted thereon, are in a close contact with a thermal grease, such that heat from the planer heat-generating element 24 is conducted to the planer evaporator 1. In this embodiment, the amount of heat generated by the planer heat-generating element 24 is about 150 W, for example. In such a case, heat of about 150 W is conducted to the planer evaporator 1 from each of the top and the bottom faces, totaling about 300 W of heat.

The above-described printed board 23 having the plurality of the electronic components 21 mounted thereon is provided in the electronic apparatus 20. Therefore, the planer evaporator 1 thermally connected to the above-described printed board 23 having the plurality of the electronic components 21 mounted thereon is provided in the cooling apparatus 22 included in the electronic apparatus 20, in order to cool the electronic components 21 included in the electronic apparatus 20. Accordingly, the planer evaporator 1 is connected to the condenser 2, the liquid reservoir tank 3, and the liquid transport pump 8 included in the cooling apparatus 22 configured as described above (see FIG. 1).

Specifically, the condenser 2 is disposed at the position about 300 mm apart from the evaporator 1. The inlet of the condenser 2 is connected to the vapor outlet 13C of the above-described planer evaporator 1 with the vapor line 4. Furthermore, the condenser 2 is fabricated by turning a copper pipe with a length of about 300 mm, an outer diameter of about 6 mm, and an inner diameter of about 5 mm, four times, for example, and swaging an aluminum radiator fin (radiator), which is not illustrated, around the copper pipe. Furthermore, a condensing device including the condenser 2 and an air-blowing fan (cooling unit, cooling means), which is not illustrated, may be provided, in order to enhance the cooling capability by blowing the air to the radiator fin, thereby providing forced air cooling. The vapor line 4 is a copper pipe having an outer diameter of about 6 mm and an inner diameter of about 5 mm. In place of the radiator fin, other types of radiators, such as a radiator plate, may be provided. Alternatively, rather than providing a radiator, cooling may be provided by directly blowing the air to the pipe. While an air-cooled cooling unit by means of the natural air convection or air blow is used in this embodiment, this is not limiting and a water-cooled cooling unit utilizing water cooling may be used. In other words, the condensing device may include a water-cooled cooling unit.

The liquid reservoir tank 3 is disposed adjacent to the above-described planer evaporator 1. The first inlet 3A of the liquid reservoir tank 3 is connected to the outlet of the condenser 2 with the liquid line 5; the second inlet 3B of the liquid reservoir tank 3 is connected to the liquid outlet 13B of the above-described planer evaporator 1 with the liquid return line 7; and the outlet of the liquid reservoir tank 3 is connected to the liquid inlet 13A of the above-described planer evaporator 1 with the liquid supply line 6 and the liquid transport pump 8. The liquid reservoir tank 3 is a tank made of a stainless-steel and having a wall of a thickness of about 0.3 mm, a bottom outer dimension of about 50 mm×about 35 mm, and a height of about 25 mm. The liquid line 5 is a copper pipe having an outer diameter of about 4 mm and an inner diameter of about 3 mm. The liquid supply line 6 is a stainless-steel pipe having an outer diameter of about 4 mm and an inner diameter of about 3 mm, while the liquid return line 7 is a copper tube having an outer diameter of about 4 mm and an inner diameter of about 3 mm. For the liquid transport pump 8, an electromagnetic piston type micro pump (model PPLP-03060-001, commercially available from Shinano Kenshi Co., Ltd.) is used, for example. Here, using ethanol as working fluid, for example, the amount of heat of about 671 J per 1 cc may be conveyed since ethanol has an evaporative latent heat amount of about 855 kJ/kg and a density of about 785 kg/m³. Assuming that an amount of heat of about 300 W (=300 J/s) is conveyed from the planer heat-generating element 24 to the planer evaporator 1, a flow rate of about 0.45 cc/sec or more is required. Therefore, the amount of liquid to be circulated by the liquid transport pump 8 is adjusted to about 0.5 cc/s (=about 30 cc/min). Note that the liquid transport pump 8 may be a piezo-driven diaphragm type pump or a centrifugal turbo pump.

Accordingly, the cooling apparatus and the electronic apparatus according to the present embodiment are advantageous in that, even if vapor bubbles are generated in liquid-phase working fluid, these vapor bubbles are easily removed, thereby achieving a stable cooling performance.

Particularly, with a cooling apparatus including a thin-planer evaporator 1 in the above-described embodiment, a planer heat-generating element that generates considerable amount of heat, such as electronic components and a printed board (circuit board), can be efficiently cooled. Furthermore, a smaller liquid transport pump 8 can be used since heat transport is achieved utilizing both the evaporative latent heat and the vapor pressure. This can enhance the performance of an electronic apparatus, such as a computer.

A printed board 23 (with a total heat generation amount of about 300 W) having operating electronic components 21 mounted thereon, was actually cooled using a cooling apparatus 22 (see FIGS. 4 and 5) that has been described as the above-described specific exemplary configuration, and the temperatures of the electronic components 21 were measured. The results indicated that all of the electronic components 21 were maintained to temperatures of about 80° C. or less, and thus a satisfactory cooling was provided.

It was also confirmed that the wick 12 in the evaporator 1 was not dried out and abnormally higher temperatures of the electronic components 21 were prevented, providing a stable cooling performance, as long as the amount of heat generated by the printed board 23 including the electronic components 21 remained within about 300 W at most.

Note that the present disclosure is not limited to the configuration of the embodiment set forth above, and may be modified in various manners without departing from the sprit of the present disclosure.

For example, a radiator may be provided in the liquid return line 7, for active heat radiation, in order to further enhance the performance of the cooling apparatus in the above-described embodiment. For example, a radiator fin or a radiator plate may be provided, as a radiator, in a portion of the liquid return line 7. Furthermore, an air-blowing fan (cooling unit, cooling means) may be provided, for blowing the air to the radiator provided in the liquid return line 7, for providing forced air for providing cooling. Alternatively, rather than providing a radiator, cooling may be provided by directly blowing the air to the liquid return line 7. While an air-cooled cooling unit by means of the natural air convection or air blow is used in this embodiment, this is not limiting and a water-cooled cooling unit utilizing water-cooling means may be used. In such a case, the cooling unit in the liquid return line 7 is separately provided from the cooling unit in the condensing device.

Furthermore, as depicted in FIG. 6, a portion of the liquid return line 7 may be provided inside a condensing device including a condenser 2 and an air-blowing fan (cooling unit, cooling means), which is not illustrated, for active heat radiation for cooling. For example, if a radiator is provided in the liquid return line 7, the portion of the liquid return line 7 wherein the radiator is disposed may be provided inside the condensing device. In such a case, the cooling unit in the condensing device may also be used as a cooling unit, such as an air-blowing fan, for cooling the liquid return line 7. Thereby, working fluid flowing through the liquid return line 7 can be cooled utilizing the cooling capability of the condensing device. Alternatively, for example, if no radiator is provided in the liquid return line 7, the liquid return line 7 is directly cooled by a cooling unit in a condensing device.

This enables active removal of vapor bubbles present in the liquid-phase working fluid flowing through the liquid return line 7. Furthermore, for example, if a greater amount of heat is conducting to the evaporator 1, the temperature of the liquid-phase working fluid flowing through the wick 12 into the liquid channel 11 tends to be increased. Even in such a case, the cooling performance can be improved by actively cooling the liquid-phase working fluid flowing through the liquid return line 7.

While the above-described embodiment has been described in the context wherein planer heat-generating elements 24 are disposed on the two surface of the planer evaporator 1, this is not limiting.

For example, as depicted in FIG. 7, a planer heat-generating element 24 is provided on one face of the planer evaporator 1 such that the planer evaporator 1 and the planer heat-generating element 24 are thermally connected to each other.

In such a case, the wick 12 may be formed as a resin porous plate including a plurality of projections 12B in a rectangular cross section which are provided on the front face side, extend in a first direction, and are arranged in parallel to each other, and a plurality of recesses 12CX in a semicircular cross section which are provided on the back face side, extend in a second direction perpendicular to the first direction, and are arranged in parallel to each other.

In such a case, it may be configured such that, once the wick 12 is enclosed in the casing 13, the surface on which the plurality of projections 12B are formed contact the top wall of the casing 13, and the surface on which the plurality of recesses 12CX are formed contact the bottom wall of the casing 13.

Thereby, a plurality of regions surrounded by the top wall of the casing 13, the side faces of the projections 12B, and the bottom faces between the plurality of projections 12B define a plurality of through holes which extend in the first direction and are arranged in parallel to each other, defining the vapor channels 10 through which vapor-phase working fluid flows. More specifically, the spaces between the plurality of projections 12B provided on the front face of the wick 12 define grooves 15, and the tops of the plurality of grooves 15 are closed with the top wall of the casing 13, defining the vapor channels 10. In addition, a plurality of regions surrounded by the bottom wall of the casing 13 and the recesses 12CX define a plurality of through holes which extend in the first direction and are arranged in parallel to each other, defining the liquid channels 11 through which liquid-phase working fluid flows. In this case, the planer heat-generating element 24 is thermally connected to the front face on which the vapor channels 10 in the planer evaporator 1 are provided. In other words, the electronic components 21 are thermally connected to the side on which the vapor channels 10 in the planer evaporator 1 are provided.

In this case, the planer evaporator 1 includes the vapor channels 10 on the upper side of the wick 12, i.e., on the side contacting the planer heat-generating element 24, and the liquid channels 11 on the bottom side of the wick 12, i.e., on the side opposite to the side contacting the planer heat-generating element 24. In other words, the planer evaporator 1 has a two-layered structure in which a vapor channel layer including a plurality of vapor channels 10 and a liquid channel layer including a plurality of liquid channels 11 are stacked. Thus, the evaporator 1 includes the vapor channels 10 provided on one of the top and bottom sides of the wick 12, and the liquid channels 11 provided on the other of the top and bottom sides of the wick 12. In this embodiment, for a planer evaporator 1, the upper vapor channel layer preferably has a height of about 1 mm or less, while the lower liquid channel layer preferably has a height of about 1 mm or less. Such a planer evaporator 1 as configured above can have a further reduced height (thickness), as compared to the above-described embodiment.

Specifically, the thickness of the wick 12, i.e., the thickness from the ends of the projections 12B on the front face to the ends of the projections 12B on the back face is about 2 mm. Furthermore, the cross-sectional height of the liquid channels 11 is about 0.5 mm. Note that other sizes are similar to those in the specific exemplary configuration of the above-described embodiment.

Furthermore, the wick 12 configured as described above includes a liquid inlet-side manifold 25 attached to one side of the liquid channels 11, and a liquid outlet-side manifold 26 attached to the other side, and is enclosed in the casing 13, as depicted in FIG. 8. More specifically, the casing 13 includes a liquid inlet 13A on one wall, a liquid outlet 13B on the wall opposing to the one wall, and a vapor outlet 13C on the wall perpendicular to the one wall. The wick 12 having the liquid inlet-side manifold 25 and the liquid outlet-side manifold 26 attached thereto is enclosed in the casing 13 such that its liquid channels 11 extend from the one wall toward the wall opposing to the one wall of the casing 13. As a result, the vapor channels 10 of the wick 12 extend from the wall perpendicular to the one wall to the opposing wall. Furthermore, the opening of the liquid inlet-side manifold 25 and the liquid supply line 6 are connected to the liquid inlet 13A of the casing 13, while the opening of the liquid outlet-side manifold 26 and the liquid return line 7 are connected to the liquid outlet 13B, and the vapor line 4 is connected to the vapor outlet 13C. In this manner, the wick 12 and the like are enclosed in the casing 13, and the liquid supply line 6 and the like are attached to the casing 13 such that the liquid supply line 6, the liquid inlet-side manifold 25, the liquid channels 11 of the wick 12, the liquid outlet-side manifold 26, and the liquid return line 7 communicate with each other, while the vapor channels 10 of the wick 12 and the vapor line 4 communicate with each other. Note that the specific constructions, such as the materials and the sizes, of the manifolds 25 and 26 and the casing 13 are similar to those in the specific exemplary configuration of the above-described embodiment.

Furthermore, as depicted in FIG. 7, the top face of the casing 13 of the planer evaporator 1 and the back face of the planer heat-generating element 24, i.e., the back face of the printed board 23 having the plurality of electronic components 21 mounted thereon, are in a close contact with a thermal grease, such that heat from the planer heat-generating element 24 is conducted to the planer evaporator 1. In this embodiment, the amount of heat generated by the planer heat-generating element 24 is about 100 W, for example. That is, the total amount of heat generated by the plurality of electronic components 21 included in the planer heat-generating element 24 is about 100 W. Therefore, this amount of heat is conducted to the planer evaporator 1.

Furthermore, similar to the above-described embodiment, the planer evaporator 1 is connected to the condenser 2, the liquid reservoir tank 3, and the liquid transport pump 8 included in the cooling apparatus 22 (see FIG. 1).

Specifically, the condenser 2 is fabricated by turning a copper pipe with a length of about 300 mm, an outer diameter of about 4 mm, and an inner diameter of about 3 mm, four times, for example, and swaging an aluminum radiator fin (radiator), which is not illustrated, around the copper pipe. The vapor line 4 is a copper pipe having an outer diameter of about 4 mm and an inner diameter of about 3 mm. The liquid line 5 is a copper pipe having an outer diameter of about 3 mm and an inner diameter of about 2 mm. The liquid supply line 6 is a stainless-steel pipe having an outer diameter of about 3 mm and an inner diameter of about 2 mm, while the liquid return line 7 is a copper tube having an outer diameter of about 3 mm and an inner diameter of about 2 mm. As depicted in FIG. 9, a piezo type micro pump (model SDMP320 available from Takasago Electric Industry Co., Ltd; with a normal flow rate of 20 ml/min, a maximum pump pressure of 35 kPa, and an outer dimension of 33 mm×33 mm×5.5 mm) is used for the liquid transport pump 8, for example. Here, using ethanol as working fluid, for example, the amount of heat of about 671 J per 1 cc may be conveyed since ethanol has an evaporative latent heat amount of about 855 kJ/kg and a density of about 785 kg/m³. Assuming that an amount of heat of about 100 W (=100 J/s) is conveyed from the planer heat-generating element 24 to the planer evaporator 1, a flow rate of about 0.15 cc/sec or more is required. Therefore, the amount of liquid to be circulated by the liquid transport pump 8 is adjusted to 0.166 cc/s (=10 cc/min). Note that the liquid transport pump 8 may be an electromagnetic piston type micro pump or a centrifugal turbo pump. Note that other constructions, such as the sizes, are similar to those in the specific exemplary configuration of the above-described embodiment.

A printed board 23 (with a total heat generation amount of about 100 W) having operating electronic components 21 mounted thereon, was actually cooled using such a cooling apparatus 22, and the temperatures of the electronic components 21 were measured. The results indicated that all of the electronic components 21 were maintained to temperatures of about 80° C. or less, and thus a satisfactory cooling was provided. It was also confirmed that the wick 12 in the evaporator 1 was not dried out and abnormally higher temperatures of the electronic components 21 were prevented, providing a stable cooling performance, as long as the amount of heat generated by the printed board 23 including the electronic components 21 remained within about 100 W at most.

Furthermore, for example, as depicted in FIG. 10, a first planer evaporator 1X and a second planer evaporator 1Y may be provided on the two faces, i.e., the top and the bottom faces, of the planer heat-generating element 24, respectively, such that the first and second planer evaporators 1X and 1Y and the planer heat-generating element 24 are thermally connected to each other. In other words, as depicted in FIG. 7 described above, the planer heat-generating element 24 may be thermally connected on a planer evaporator 1, and another planer evaporator 1 may be thermally connected on the planer heat-generating element 24.

In such a case, the first and second planer evaporators 1X and 1Y include vapor channels 10 on the sides contacting the planer heat-generating element 24, and liquid channels 11 on the sides opposing to the sides contacting the planer heat-generating element 24. Thus, the first planer evaporator 1X includes the vapor channels (first vapor channels) provided on one of the top and bottom sides of the wick 12 (first porous body), and liquid channels 11 (first liquid channels) provided on the other of the top and bottom sides of the wick 12. Furthermore, the second planer evaporator 1Y includes the vapor channels 10 (second vapor channels) provided on one of the top and bottom sides of the wick 12 (second porous body), and liquid channels 11 (second liquid channels) provided on the other of the top and bottom sides of the wick 12. The side on which the vapor channels 10 in the first planer evaporator 1X is provided are thermally connected to the back face side of the electronic components 21, and the side on which the vapor channels 10 in the second planer evaporator 1Y are provided is thermally connected to the front face side of the electronic components 21. Note that the configuration and a specific exemplary configuration of the first and second planer evaporators 1X and 1Y are similar to those in the planer evaporator 1 depicted in FIG. 7 and FIG. 8 described above.

Furthermore, as depicted in FIG. 10, the top face of the casing 13 of the first planer evaporator 1X, i.e., the front face of the casing 13 on the vapor channel 10 side and the bottom face of the planer heat-generating element 24, i.e., the back face of the printed board 23 having the plurality of electronic components 21 mounted thereon, are in a close contact via a thermal grease. Furthermore, the bottom face of the casing 13 of the second planer evaporator 1Y, i.e., the front face of the casing 13 on the vapor channel 10 side and the top face of the planer heat-generating element 24, i.e., the front face of the printed board 23 having the plurality of electronic components 21 mounted thereon, are in a close contact via a thermal grease. Thereby, heat from the planer heat-generating element 24 is conducted to the upper and lower first and second planer evaporators 1X and 1Y. In this embodiment, the amount of heat generated by the planer heat-generating element 24 is about 200 W, for example. That is, the total amount of heat generated by the plurality of electronic components 21 included in the planer heat-generating element 24 is about 200 W. Therefore, this amount of heat is conducted to the upper and first and second planer evaporators 1X and 1Y.

Furthermore, the first and second planer evaporators 1X and 1Y are connected to the condenser 2, the liquid reservoir tank 3, and the liquid transport pump 8 included in the cooling apparatus 22, as depicted in FIG. 11.

In this embodiment, the vapor line 4 connected to the condenser 2 is branched into two tubes, which are connected to the first and second planer evaporators 1X and 1Y, respectively. More specifically, the vapor line 4Y connected to the second planer evaporator 1Y is connected to the vapor line 4X connecting the condenser 2 and the first planer evaporator 1X.

Furthermore, the liquid return line 7 connected to the liquid reservoir tank 3 is branched into two tubes, which are connected to the first and second planer evaporators 1X and 1Y, respectively. More specifically, the liquid return line 7Y connected to the second planer evaporator 1Y is connected to the liquid return line 7X connecting the liquid reservoir tank 3 and the first planer evaporator 1X.

Furthermore, the liquid supply line 6 connected to the liquid reservoir tank 3 via the liquid transport pump 8 is branched into two tubes, which are connected to the first and second planer evaporators 1X and 1Y, respectively. More specifically, the liquid supply line 6Y connected to the second planer evaporator 1Y is connected to the liquid supply line 6X connecting the liquid reservoir tank 3 and the first planer evaporator 1X via the liquid transport pump 8.

Thus, the first planer evaporator 1X and the second planer evaporator 1Y are connected to each other in parallel. In other words, a route defined by the liquid supply line 6Y, the second planer evaporator 1Y, and the vapor line 4Y is connected to a route defined by the liquid reservoir tank 3, the liquid supply line 6X, the first planer evaporator 1X, the vapor line 4X, the condenser 2, and the liquid line 5 in parallel. Furthermore, a route defined the liquid reservoir tank 3, the liquid supply line 6X, the first planer evaporator 1X, and the liquid return line 7X is connected to a route defined the liquid supply line 6Y, the second planer evaporator 1Y, and the liquid return line 7Y in parallel.

Note that the above configuration is not limiting, and the first planer evaporator 1X and the second planer evaporator 1Y may be connected in series. More specifically, the liquid return line 7X connected to the outlet of the liquid channels 11 in the first planer evaporator 1X may be connected to the inlet of the liquid channels 11 in the second planer evaporator 1Y, in place of the liquid supply line 6Y, while the liquid return line 7Y connected to the outlet of the liquid channels 11 in the second planer evaporator 1Y may be connected to the liquid reservoir tank 3, in place of the liquid return line 7X. In this case, the vapor lines 4 (4X and 4Y) connected to the condenser 2 are connected to the first and second planer evaporators 1X and 1Y, respectively. Furthermore, the liquid supply line 6 (6X) connected to the liquid reservoir tank 3 via the liquid transport pump 8 is connected to the inlet of the liquid channels 11 in the first planer evaporator 1X. Furthermore, the liquid supply line 6 (6Y) connected to the inlet of the liquid channels 11 in the second planer evaporator 1Y is connected to the outlet of the liquid channels 11 in the first planer evaporator 1X. Furthermore, the liquid return line 7 (7Y) connected to the outlet of the liquid channels 11 in the second planer evaporator 1Y is connected to the liquid reservoir tank 3. Thereby, after being supplied from the liquid reservoir tank 3 to the first planer evaporator 1X through the liquid supply line 6X, liquid-phase working fluid is supplied to the second planer evaporator 1Y through the liquid return line 7X as a liquid supply line, and is returned to the liquid reservoir tank 3 through the liquid return line 7Y.

For the liquid transport pump 8, an electromagnetic piston type micro pump (model PPLP-03060-001, commercially available from Shinano Kenshi Co., Ltd.) is used, for example (see FIG. 3). Here, using ethanol as working fluid, for example, the amount of heat of about 671 J per 1 cc may be conveyed since ethanol has an evaporative latent heat amount of about 855 kJ/kg and a density of about 785 kg/m³. Assuming that an amount of heat of about 200 W (=200 J/s) is conveyed from the planer heat-generating element 24 to the first and second planer evaporators 1× and 1Y, a flow rate of about 0.3 cc/sec or more is required. Therefore, the amount of liquid to be circulated by the liquid transport pump 8 is adjusted to 0.333 cc/s (=20 cc/min). Note that the liquid transport pump 8 may be a piezo-driven diaphragm type pump or a centrifugal turbo pump.

Note that other specific constructions, such as dimensions, are similar to the case in which the planer evaporator 1 depicted in FIGS. 7 and 8 described above.

Furthermore, while a portion of the liquid return line 7 is provided inside a condensing device including the condenser 2 and an air-blowing fan (cooling unit, cooling means), which is not illustrated, thereby providing active heat radiation for cooling in FIG. 11, this is not limiting and the configuration similar to those in the above-described embodiment (see FIG. 1) may be used.

A printed board 23 (with a total heat generation amount of about 200 W) having operating electronic components 21 mounted thereon, was actually cooled using such a cooling apparatus 22, and the temperatures of the electronic components 21 were measured. The results indicated that all of the electronic components 21 were maintained to temperatures of about 80° C. or less, and thus a satisfactory cooling was provided. It was also confirmed that the wicks 12 in the evaporators 1X and 1Y were not dried out and abnormally higher temperatures of the electronic components 21 were prevented, providing a stable cooling performance, as long as the amount of heat generated by the printed board 23 including the electronic components 21 remained within about 200 W at most.

Particularly, since the height (thickness) of the first and second planer evaporators 1X and 1Y as described above can be reduced even further than that of the above-described embodiment, the first and second planer evaporators 1X and 1Y may be provided over both the top and bottom of a heat-generating element 24. Therefore, heat-generating element 24 that generates a large amount of heat, such as a 3D stacked package for achieving higher-density packaging, for example, can be effectively cooled.

For example, as depicted in FIGS. 12A and 12B, a 3D stacked package 30 is a three-dimensional stacked package (LSI package) including a plurality of semiconductor chips 31 and 31X (LSI chips) that are stacked three-dimensionally. Thus, as depicted in FIG. 12A, even in a case where a planer evaporator 1 of the above-described embodiment is provided on the 3D stacked package 30, which is then mounted on a printed board (circuit board) 23, sufficiently radiating heat generated by the semiconductor chip 31X located on the bottom side, i.e., on the printed board 23 side, is difficult. To address this issue, as depicted in FIG. 12B, by providing the first planer evaporator 1X on the back face side of the printed board 23, together with the second planer evaporator 1Y on the front face side of the 3D stacked package 30, heat generated by the semiconductor chips 31 and 31X included in the 3D stacked package 30 can be effectively radiated. In such a case, as described above, by using thinner first and second planer evaporators 1X and 1Y, heat generated by the semiconductor chips 31 and 31X included in the 3D stacked package 30 can be more effectively radiated, as compared to the structure depicted in FIG. 12A, without increasing the height of the package when mounted.

While the vapor channels 10 and the liquid channels 11 in the evaporator 1 extend in the directions perpendicular to each other in the above-described embodiment, this is not limiting. For example, as depicted in FIG. 13, the vapor channels 10 and the liquid channels 11 in the evaporator 1 may be provided so as to extend in the same direction.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such For example recited examples and conditions, nor does the organization of such examples in the specification relate to a illustrating of the superiority and inferiority of the invention. Although the embodiments have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 

1. A cooling apparatus comprising: an evaporator, comprising a porous body, a vapor channel and a liquid channel separated by the porous body, to evaporate a working fluid in liquid phase; a condenser to condense the working fluid in vapor phase; a liquid reservoir tank to reserve the working fluid in the liquid phase; a vapor line connecting an outlet of the vapor channel in the evaporator and an inlet of the condenser; a liquid line connecting an outlet of the condenser and a first inlet of the liquid reservoir tank; a liquid supply line connecting an outlet of the liquid reservoir tank and an inlet of the liquid channel in the evaporator; a liquid return line connecting an outlet of the liquid channel in the evaporator and a second inlet of the liquid reservoir tank; and a liquid transport unit interposed in the liquid supply line.
 2. The cooling apparatus according to claim 1, wherein the porous body is a porous body formed from a resin.
 3. The cooling apparatus according to claim 1, wherein the liquid return line comprises a radiator.
 4. The cooling apparatus according to claim 1, further comprising a condensing device comprising the condenser and a cooling unit, wherein a portion of the liquid return line is provided inside the condensing device.
 5. The cooling apparatus according to claim 1, wherein the second inlet of the liquid reservoir tank is provided farther from the outlet of the liquid reservoir tank than the first inlet.
 6. The cooling apparatus according to claim 1, wherein the vapor channel and the liquid channel extend orthogonally from each other.
 7. The cooling apparatus according to claim 1, wherein the vapor channel comprises a first vapor channel provided over a top side of the porous body, and a second vapor channel provided over a bottom side of the porous body, and the liquid channel is a liquid channel provided inside the porous body.
 8. The cooling apparatus according to claim 1, wherein the vapor channel is a vapor channel provided over one of top and bottom sides of the porous body, and the liquid channel is a liquid channel provided over the other of the top and bottom sides of the porous body.
 9. The cooling apparatus according to claim 1, wherein the porous body has an average pore diameter of about 10 μm or less.
 10. An electronic apparatus comprising: an electronic component provided over a circuit board; and a cooling apparatus to cool the electronic component, the cooling apparatus comprising: an evaporator, comprising a porous body, a vapor channel and a liquid channel separated by the porous body, to evaporate a working fluid in liquid phase; a condenser to condense the working fluid in vapor phase; a liquid reservoir tank to reserve the working fluid in the liquid phase; a vapor line connecting an outlet of the vapor channel in the evaporator and an inlet of the condenser; a liquid line connecting an outlet of the condenser and a first inlet of the liquid reservoir tank; a liquid supply line connecting an outlet of the liquid reservoir tank and an inlet of the liquid channel in the evaporator; a liquid return line connecting an outlet of the liquid channel in the evaporator and a second inlet of the liquid reservoir tank; and a liquid transport unit interposed in the liquid supply line, wherein the electronic component is thermally connected to the evaporator.
 11. The electronic apparatus according to claim 10, wherein the porous body is a porous body formed from a resin.
 12. The electronic apparatus according to claim 10, wherein the liquid return line comprises a radiator.
 13. The electronic apparatus according to claim 10, further comprising a condensing device comprising the condenser and a cooling unit, wherein a portion of the liquid return line is provided inside the condensing device.
 14. The electronic apparatus according to claim 10, wherein the second inlet of the liquid reservoir tank is provided farther from the outlet of the liquid reservoir tank than the first inlet.
 15. The electronic apparatus according to claim 10, wherein the vapor channel comprises a first vapor channel provided over a top side of the porous body, and a second vapor channel provided over a bottom side of the porous body, and the liquid channel is a liquid channel provided inside the porous body.
 16. The electronic apparatus according to claim 15, wherein the electronic component comprises a first electronic component thermally connected to a top side of the evaporator, and a second electronic component thermally connected to a bottom side of the evaporator.
 17. The electronic apparatus according to claim 10, wherein the vapor channel is provided over one of top and bottom sides of the porous body, and the liquid channel is provided over the other of the top and bottom sides of the porous body.
 18. The electronic apparatus according to claim 17, wherein the electronic component is thermally connected to the side where the vapor channel in the evaporator is provided.
 19. The electronic apparatus according to claim 10, wherein the evaporator comprises: a first evaporator comprising a fist porous body, a first vapor channel provided over one of top and bottom sides of the first porous body, and a first liquid channel provided over the other of the top and bottom sides of the first porous body; and a second evaporator comprising a second porous body, a second vapor channel provided over one of top and bottom sides of the second porous body, and a second liquid channel provided over the other of the top and bottom sides of the second porous body, wherein the side where the vapor channel in the first evaporator is provided is thermally connected to a back face side of the electronic component, and the side where the vapor channel in the second evaporator is provided is thermally connected to a front face side of the electronic component.
 20. The electronic apparatus according to claim 10, wherein the porous body has an average pore diameter of about 10 μm or less. 